This invention relates to a semiconductor laser device and, more particularly, to a semiconductor laser driver having an automatic light output stabilizer circuit, which detects the intensity of the laser beam, emitted from a semiconductor laser and controls the drive current to the semiconductor laser to maintain a constant laser beam intensity.
The semiconductor laser has a non-linear laser output characteristic with respect to the drive current (or drive voltage) and is susceptible to the influence of ambient temperature. To obtain a constant laser output, the semiconductor laser is driven by a driver having an automatic output stabilizer (hereinafter referred to as APC). A laser beam emitted from the back side of the semiconductor laser is detected by a PIN type photodiode. According to the quantity of detected light a closed loop feedback circuit is formed to maintain a constant semiconductor laser beam output intensity level.
However, when the photodiode itself is not operating properly, normal feedback control can not be obtained, and stabilization of the output beam intensity can not be obtained. Where the semiconductor laser is used for a pick-up of an optical recording/reproducing apparatus, accurate recording and reproduction of data can not be obtained.
Further, when normal feedback control can not be obtained, an excessive drive current flows through the semiconductor laser, and deterioration or rupture of the semiconductor laser is liable to result.
Further, since the semiconductor laser driver inclusive of the APC circuit is complicated in construction, even in case of operating difficulties due to mere deterioration or defectiveness of a photodiode, it takes time to, that is, trouble shoot the mean time to repair (MTTR) as an indicator of the reliability of the apparatus is extended.